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ויהי בבקר והנה היא לאה, כי עד הבקר לא הכיר בה כמו שפירשנו, והדרש שמסרה לה רחל סימנים ידוע: ויהי בבוקר והנה היא לאה, for he had not recognised her until morning as we explained. The aggadic explanation mentioned by Rashi that Rachel had given her sister Leah the codeword which she and Yaakov had agreed should serve to preclude such a swap is well known.